WRPS retrieving a record three tanks at once

For the first time, waste solids are in the process of being retrieved simultaneously from three underground tanks: C-104, C-107 and C-109.

"Retrieving waste from the tanks remains a top priority for the Office of River Protection. WRPS is simultaneously retrieving waste from three tanks and performing construction activities on two additional tanks," said Joanne Grindstaff, Federal Project Director for Single Shell Tank Retrieval and Closure. "Their employees continue to perform work safely while efforts in the tank farm have increased."

Crews are working to remove the last bit of hard heel waste from C-104. On Tuesday, June 26, crews began a four-week recirculation of caustic in the tank after 15,000 gallons of sodium hydroxide were added the previous week to begin dissolution of the remaining hard heel. During the recirculation period, the caustic will react with the gibbsite to create a water-soluble salt. After the reaction is complete, the remaining material will be pumped to double-shell tank AN-101 and C-104 will undergo a final rinse.

To date, crews have used modified sluicing and hot water washes to remove more than 98 percent of the 259,000 gallons of waste C-104 contained when retrieval began in January 2010. The Tri-Party Agreement requires that 99 percent of the waste is removed from the single-shell tanks or certain criteria are met regarding limits of technology.

Meanwhile, the Mobile Arm Retrieval System (MARS) marches on in tank C-107, having removed nearly 66 percent of the tank's contents. MARS' robotic arm is equipped with a built-in cannon which uses recirculated tank waste to mobilize and break up waste in the tank and sweep it to a pump for removal. Its mobility has allowed operators to quickly and skillfully maneuver around obstacles found in the tank that would normally set back retrieval efforts a number of weeks.

A third tank, C-109, is in the middle of a water soak aimed to loosen and break down waste solids into a mobile form. Recent sampling shows the hard-to-remove heel is dissolving and slurry pump activities are forecast to occur in July or August. It's estimated that less than 14 percent of the original starting volume of 63,000 gallons remains in the tank.

All this activity is in addition to the completion of retrieval activities earlier this year in tank C-108, which is awaiting review by the Department of Ecology.

"Activities in the tank farm will continue at this pace as we work towards retrieving waste from the remaining tanks in C Farm to meet the Consent Decree milestone by September 2014, reducing the risk to the public and environment," saidGrindstaff.